Field of the Invention
The invention relates to a sheet guiding device in a machine for processing sheets of printing material, which have unthrottled air nozzles for guiding the sheets in a contact-free manner.
The published German Patent Document DE 19628 620 A1 describes such a guiding device which serves for guiding freshly printed sheets and which includes a first nozzle configuration having blast air nozzles for generating air jet beams and a second nozzle configuration having blast air nozzles for generating torsional flows. In an exemplifying embodiment, a nozzle body with helical channels, which is constructed as a cylindrical cup or bowl with a worm fitted therein, is connected to a blast air nozzle of the second nozzle configuration body, at a location upline therefrom. The channels, which are helically rather than spirally formed, cause virtually no throttling of the blast air.
A disadvantage of the aforedescribed guiding device is that the torsional flow is not optimally effective under all operating conditions, and the flow intensity must be readjusted whenever there are changes in the conditions, such as a change in the printing material, for example. If this readjustment should occur imprecisely or too late, there is a danger of smearing the freshly printed sheet at locations of the guiding device which are susceptible or prone to contact.
The state of the prior art additionally includes a guide mechanism as described in the published German Patent Document DE 198 29 094 A1, which has porous guide surfaces by which diffuse airflows can be generated. This guide mechanism is operable module by module in a suction mode, so that suction and a frictional, i.e., gliding, transport of the sheet along a respective guide surface can occur in problem areas of the sheet guiding system. This technical solution thus purposely deviates from the principle of contact-free sheet guidance.
The side of the sheet which is acted upon by the suction can slide on the guide surface, without smearing, only if this side is unprinted.
It is accordingly an object of the invention to provide a sheet guiding device of the general type described in the introduction hereto, which ensures contact-free sheet transport even under changing operating conditions, and which is particularly well suited for guiding sheets which have been freshly printed on both sides thereof.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a guiding device in a machine for processing sheets of printing material, comprising unthrottled air nozzles for contact-freely guiding the sheets, and throttled air nozzles arranged at locations which are prone to contact by the sheets.
In accordance with another feature of the invention, the throttled air nozzles are located at a contact-prone curve of a guide surface.
In accordance with a further feature of the invention, the throttled air nozzles are located at a contact-prone end region of a guide surface.
In accordance with an added feature of the invention, the unthrottled air nozzles are pneumatically connected by way of a first air conducting system, and the throttled air nozzles are pneumatically connected by way of a second air conducting system, for providing a prevailing air pressure p1 in the first air conducting system which is less than an air pressure P2 prevailing in the second air conducting system.
In accordance with an additional feature of the invention, at least one of the throttled air nozzles is assigned to an air throttle.
In accordance with yet another feature of the invention, the air throttle includes a fill.
In accordance with yet a further feature of the invention, the air throttle includes a filter-type throttle piece.
In accordance with yet an added feature of the invention, the air throttle is formed with a spiral air channel.
In accordance with yet an additional feature of the invention, the air throttle includes protruding air barriers and eddy chambers located therebetween.
In accordance with still another feature of the invention, the air throttle includes perforated plates disposed on top of one another, with eddy chambers located therebetween.
In accordance with still a further feature of the invention, the throttled air nozzles are blast air nozzles.
In accordance with still an added feature of the invention, the unthrottled air nozzles are blast air nozzles.
In accordance with another aspect of the invention, there is provided a machine for processing sheets of printing material having at least one sheet guiding device, comprising unthrottled air nozzles for contact-free guidance of the sheets, and throttled air nozzles arranged at locations which are prone to contact by the sheets.
In accordance with a further feature of the invention, the guiding device is integrated into a sheet delivery.
In accordance with a concomitant aspect of the invention, there is provided a sheet-fed rotary printing machine having at least one sheet guiding device, comprising unthrottled air nozzles for contact-free guidance of sheets, and throttled air nozzles arranged at locations which are prone to contact by the sheets.
A blast or blowing force which is exerted by each of the throttled air nozzles upon the sheets increases overproportionately, i.e., more than linearly, as the distance of the sheet from the respective air nozzle decreases. Thus, it is possible to generate an air cushion between the sheet and a guide surface of the guiding device, the guide surface being provided with the throttled air nozzles, which holds the sheet at a spaced distance from the guide surface much more reliably than is possible with unthrottled air nozzles.
An additional advantage is in the small volume flow generated by the throttled air nozzles, because the infiltrated or leaked air flow generated by the throttled air nozzles which are not covered by the sheet (dependent upon the format) is consequently rather small and does not have to be blocked.
In developments which are advantageous with respect to the realization of the sheet guiding device, including a guide surface in a sheet delivery, the contact-prone locations are provided at a curve or an end region of the guide surface. The guided sheet is prevented completely for all practical purposes from engaging or stopping at the guide surface, even in the region of the contact-prone locations of the guide surface, by the influence of the throttled air nozzles upon the sheet.
In a development which is advantageous with respect to the realization of the unthrottled air nozzles as conventional impulse-blast nozzles, e.g., venturi nozzles or torsion jet nozzles, the unthrottled air nozzles are chargeable with excess pressure by way of a first air conducting system, and the throttled air nozzles are chargeable with excess pressure by way of a second air conducting system, the excess pressure of the unthrottled air nozzles being less than the excess pressure of the throttled air nozzles.
In a separate development, each of the throttled air nozzles is connected to an air pressure generator by way of an air throttle. The air throttle can be integrated into the second air conducting system distal from the respective throttled air nozzle. This is expedient when providing an air throttle which is pneumatically connected to several throttled air nozzles simultaneously by way of the second air conducting system. The air throttle and the air nozzle throttled thereby can also be constructed as a single unit in the form of a throttle nozzle. In this case, a separate air throttle is assigned to each of the throttled air nozzles.
In a further development, a so-called fill column forms an internal component of the air throttle, the fill elements thereof forming flow resistors for the blast air which is generated by the air pressure generator and which flows through the air throttle.
In a separate development, an airfilter-type throttle piece is an internal component of the air throttle and forms a flow resistor for the blast air. For example, the throttle piece may be a textile layer which may or may not be woven. The throttle piece may also be a porous and, therefore, air-permeable sponge foamed from a plastic material.
In a separate embodiment, the air throttle contains air barriers which protrude into the flow path of the blast air and which define eddy chambers.
In a separate development, the air throttle is constructed as a so-called perforated plate maze or labyrinth.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a sheet guiding device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: